1. Field of the Invention
The present invention relates to an image capturing apparatus capable of changing its image capturing direction in a state where a body of the image capturing apparatus is fixed.
2. Description of the Background Art
Since a surveillance camera used by being mounted on the wall, the ceiling or the like of a room has to monitor a wide range, usually, the image capturing direction of the camera can be freely changed by the driving of various motors or the like by a remote control or the like.
Conventionally, such a surveillance camera is turnable around two axes of the horizontal axis and the vertical axis. For example, in the case of using a pulse motor as a drive source for turning the camera around each of the horizontal and vertical axes, by controlling the turn amount in the turn direction around the horizontal axis as a center (hereinafter, referred to as “tilting direction”) and the turn amount in the turn direction around the vertical axis as a center (hereinafter, referred to as “panning direction”) in accordance with the number of pulses given to the pulse motors, a change in the image capturing direction can be easily controlled.
However, generally, depending on the drive frequency, that is, the pulse rate (the number of pulses given per second, hereinafter, the unit will be abbreviated as “pps”) given to a pulse motor, the drive source such as a pulse motor generates resonance with a body of the surveillance camera or the like and noise generates. Consequently, since it is desirable to reduce noise sound as much as possible in a quiet room or the like, the drive source is driven generally on the basis of a pulse rate lower than the drive frequency at which resonance is caused (hereinafter, referred to as “resonance frequency”).
There are mainly two types of operating the surveillance camera. One of the types is a type of instructing only the driving direction and the other type is a type of directly instructing a target direction.
In the operation method of the former type, for example, by tilting an operation lever to a desired direction, the image capturing direction can be changed to the instructed direction. In order to stop the changing of the image capturing direction, it is sufficient to move the operation lever to the original position. In the operation method, the user has to operate the lever while watching a captured image and, when the image capturing direction reaches a desired direction, move the lever to the original position to stop the changing of the image capturing direction. When the changing speed of the image capturing direction is too fast, it is difficult to perform an accurate operation. Therefore, it is desirable to change the image capturing direction slowly.
On the other hand, in the operation method of the latter type, for example, a chart indicating a changeable range of the image capturing direction and the present image capturing direction are displayed on the screen of a personal computer or the like. By moving a cursor to a desired image capturing direction (target direction) and clicking the mouse, the image capturing direction can be automatically changed to the instructed target direction. In the operation method, when the target direction is directly designated, a turn in the panning direction and a turn in the tilting direction are simultaneously started and simultaneously completed, thereby enabling the image capturing direction to be changed to the designated target direction as fast as possible. Consequently, a time lag in changing of the image capturing direction is short and the operability is good.
In the operation method of the latter type, however, in order to change the image capturing direction to the target direction as fast as possible, when a pulse rate is simply changed, depending on the changing direction of the image capturing direction, the pulse rate given to one of the two pulse motors may enter the resonance frequency range and it causes large noise sound at the time of changing of the image capturing direction.
As a technique of suppressing the noise which will be generated during changing of the image capturing direction, a noise preventing technique has been proposed, which suppresses noise caused by resonance resulting from vibration of an intermediate gear during changing of the image capturing direction by inserting a friction member into the intermediate gear for transmitting a driving force of a stepping motor to prevent vibration of the gear (for example, Japanese Patent Application Laid-Open No. 10-9367 (1998)).
However, since the resonance which generates during changing of the image capturing direction due to the motor itself is larger than the resonance which generates due to the gear, only by the countermeasure of suppressing the resonance which generates due to the gear like the above-described noise preventing technique, generation of the resonance during changing of the image capturing direction, that is, generation of noise cannot be sufficiently suppressed.